The embodiments described herein relate generally to photoacoustic scanning methods and apparatus and, more particularly, to a method and a system for determining an optical absorption coefficient by an object using acoustic spectra.
Total, oxygenated, and deoxygenated hemoglobin concentrations ([HbT], [HbO2], and [HbR], respectively) are fundamental pathophysiological parameters in biomedicine. For example, abnormally low [HbT] may be caused by loss of blood, nutritional deficiency, chemotherapy, inflammation, kidney failure or bone marrow problems, while abnormally high [HbT] may be related to exposure to high altitude, smoking, dehydration and tumors. Blood oxygen saturation (sO2), which is defined as [HbO2] divided by [HbT], is vital in understanding brain hemodynamics in response to sensory stimulations, monitoring healing of burns and wounds, and evaluating the effectiveness of chemotherapy and radiotherapy on tumors. Several techniques have been developed to quantify hemoglobin concentration and sO2 in vivo, including near-infrared spectroscopy (NIRS), blood oxygen level dependent (BOLD) contrast magnetic resonance imaging (MRI), electron paramagnetic resonance imaging (EPRI), positron emission tomography (PET), and single photon emission computed tomography (SPECT). However, all of these modalities have disadvantages. For example, at least some of these modalities have poor spatial resolution, relative quantification, and undesirable contrast agent injection. Photoacoustic (PA) tomography (PAT) has already demonstrated its ability to monitor biological hemodynamic functions without using exogenous contrast agents. Quantitative PAT is challenging, because compensating for the fluence in quantitative in vivo photoacoustic tomography is difficult, and factors, such as the tissue acoustic attenuation and the imaging system bandwidth, also affect the quantification accuracy.